If sales increased by 15% next year the net income will increase by $90,000

a)New Fixed Cost * 90%

= 400,000 * 0.90

= 360,000

N.I. ( S- VC )x – FC

= (1 -0.50)* 1,200,000 – 360,000

= 600,000 – 360,000

Net Income = 240,000

240,000 – 200,000 = 40,000

The Net Income increases by 40,000

b)IF variable costs are 10% higher in the year ahead (but sales and fixed costs remain the same as last year), how much (in$) will the net income decrease?

Your work is very hard to follow. I am not even sure where your question is.

For part a, you'll notice that variable costs are half of sales or $0.50 on the dollar. So, break even is

For part b, sales would increase by Half of this is lost to variable costs, so net income increase by 90000

For part c, fixed costs decrease by 10% and income will increase by the amount of this decrease because no other changes have occurred. Thus income increases

For part d, Instead of being 50% of sales they will increase to and income will decrease by the amount of their increase. Thus income will decrease by 5% or . Alternatively, income decreases by 10% of variable costs